Boron is a Group IIIA element having properties between a metal and non-metal. Boron has unique characteristics of being: a) a hard, refractory solid; b) a metalloid; c) a semiconductor; d) light weight; e) high strength; f) high melting; g) a solid fuel material; h) and reactive with metals. Because of these unique characteristics, boron has industrial applications in the areas of ceramics, propulsions, pyrotechnics, metallurgy, nuclear, medical, and electronics to name a few. However, the unique characteristics of boron make it difficult to prepare elemental boron.
A method for preparing elemental boron by electrolysis of B2O3 in a molten salt of MgO and MgF2 at 1100 degrees Celsius was reported by Andrieux in “Recherches sur l'électrolyse des Oxydes Métalliques Dissous dans L'ánhydride Borique ou dans les Borates Fondus: Nouvelles Méthodes de Préparation du Bore Amorphe, des Borures et de Quelques Métaux” (Ann. de Chim., 10 (12): 423-462, 1929). The electrochemical produced boron contained magnesium as its main impurity.
U.S. Pat. No. 2,909,471 to Nies (hereafter Nies '471) discussed electrochemical production of elemental boron from an electrolyte containing KF, MgF2, and B2O3, the entire contents of which is incorporated herein by this reference. The elemental boron contained appreciable quantities of magnesium. Nies '471 further described electrolytes comprising KCl—KF—K2O—B2O3, KCl—KBF4—B2O3, and KCl—NaCl—NaF—B2O3.
U.S. Pat. No. 2,832,730 to Nies (hereafter Nies '730) indicated optimal electrochemical production of elemental boron occurred in KCl—KF—B2O3 mixtures containing 10 wt % of B2O3, which is incorporated herein by reference in its entirety. The electrolysis was conducted between 775 to 925 degrees Celsius. Nies '730 further indicated poor electrode adhesion of elemental boron occurred in KCl—KF—B2O3 mixtures having less than 10 wt % B2O3 and mixtures having more than 10 wt % B2O3 were too viscous for electrolysis.
U.S. Pat. No. 2,984,605 to Cooper (hereafter Cooper) discussed electrochemical production of elemental boron from an electrolyte comprising KBF4 and B2O3, which is incorporated herein by this reference in its entirety. The electrolyte contained between 2 to 15 wt % B2O3. The electrolysis was conducted between 600 to 750 degrees Celsius and produced oxygen and the elemental boron.
Yukin reported forming elemental boron by electrolyzing Na2B4O7 (“Mechanisms of Electroplating with Boron” Metalloved. Term. Obrad. Met., 8: 42, 1971). The electrolysis produced sodium, which reacted with B4O72− to produce elemental boron.
A three electron cathodic reduction of BF4− in LiF—KF—KBF4 and LiF—KF—B2O3 melts was reported by Makyta et al. in “Mechanism of the Cathode Process in the Electrolytic Boriding in Molten Salts” (Electrochimica Acta., 29 (12): 1653-1657, 1984). The three electron cathodic reduction process is represented by the following chemical half-cell reaction:BF4−+3e−B0+4F−  (1)Moreover, Makyta et al. reported the B2O3 reacted with LiF—KF to form KBF4, which formed elemental boron according to equation (1).
According to Polyakova, B3+ is reduced to elemental boron in a single irreversible step in LiF—NaF—KF melts containing less than 5.7×10−2 mole per cent of KBF4 (“Electrochemical Behavior of Boron in LiF—NaF—KF Melts” published in J. Electrochem. Soc., 143 (1): 3178-3186, 1996).
A need exists for preparing higher purity elemental boron more efficiency. A further need exists for preparing elemental boron at lower temperatures and/or with less current density. Moreover, an environmentally friendly process is needed.